Method of making magnetic cores



Oct. 13, 1931. R. c. SHERMUND 1,327,375

METHOD OF MAKING MAGNETIC CORES Filed Oct. 3. 192a l N V EN TOR Pal 0h C. Shermund A TTORNEYS ,Patented o... 13, 1931 v UNIT-EDt-STATES TE FFICE RALPH C. SHERMUND, OF PALO ALTO CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, CORPORATION OF CALI- FORN'IA METHOD or MAKING macnmrc oonEs Application filed October 3, 1828. Serial No. 309,967.

This invention relates position of matter in soli form particularly adapted for use as a magnetic core material, and to methods of manufacturing the same.

I It is a general object of this invention to provide a composition of matter having relatively high magnetic permeability, low hysteresis and eddy current losses, of suificient mechanical strength to form a self supportm ing structure. v

A feature of the invention is a magnetic core composed of finely divided particles of a magnetlc metal or alloy separated by a heat resistant binding and insulating substance 1! whereby the core may be exposed to high temperature without altering either its electrical and magnetic properties or its mechanical stren h. 7

Re erring to the drawin s':

Figure '1 is a plan view lllustrating a convenient form for my composition.

Figure 2 is a side view of the form shown in Fig. 1, a portion of the material being broken away; 1

Figure 3 is a side elevational view of an assembled magnetic coreformed of a lurality of'members such as shown in. igs. 1 and 2..

. o It has reviously been proposed to utilize If fusible blnding materials, such as various phenol condensation products, in the manu-' facture of solid compositions containing comminuted metallic materials. For various reasons the 'us'e of binding materials of this.

character is often undesirable, as for example, they cannot withstand the temperatures to which the finished product should be heated for annealingpurposes. The composition and method of this invention is the result of the discovery that mica when in proper condition can be em loyed alone with-' out other binding .materia s as a means for retaining divided metallic material in solid form. Mica is not only readily available at withstanding relatively high temperatures.

'In compositions in accordance with this generally to a comlow cost, but is a material which is capable of of thecomposition, such as a divided metallic material, is mixed with the mica by grinding them together. The resulting mixture is subected to high pressure whereby it is transformed into a solid mass having considerable mechanical strength.

As the compositions are' particularly useful for magnetic cores, the preferred embodiment of theinvention utilizes finely divided mica together with a comminuted magnetic material such as iron, nickel or an iron nickel alloy. A composition of good permeability has been obtained by using eight to ten per cent of mica with the balance" finely divided iron. The iron and mica are individually ground to a sufiicient fineness to ss a-100 mesh screen, and are then intro uced into a ball mill and are ground together and thoroughly intermixed. Durin this inter- ,mixing and grinding the particles of iron apparently become coated by the minute articles of mica. The resultin mass is t en introduced into a press where it is compressed to solid form by a pressure of say 200,000

76 position when removed from the press, can

pounds per square inch. The resulting comaperture 11. Referring to Fig.3 a plurality of these members 10 are shown assembled upon an insulating rod- 12 to form a cylindrical magnetic core 13.

The composition produced by the process of this invention is not only cheap and simple to manufacture, but its magnetic qualities are such that it can be employed to form cores of high frequency inductances, such as are employed in radio apparatus.

The mica utilized in the composition not only serves as a binding means, but also elecf tricallyinsulates the metallic particles from each other. Therefore losses due to eddy currents are minimized when the composition is employed as a core for a varying magnetic .fiel 4 i 2 nan-nave I claim:

1. The method of making a ma etic core which com rises grinding toget er finel comminute magnetic material and mice. an

5 compressing the resultant mass into a. self sustaining solid.

2. The method of making a ma etic core which comprises grinding toget er finel comminuted magnetic material and mica ans compressing the resultant mixture into a self sustaining solid. 3.. The method of making a ma etic core which com rises grinding togetfiier finel comminute magnetic material and mica an 15 compressing the resultant mixture into a self sustaining solid under a pressure of at least 150,000 pounds per square inch. 7

In testimony whereof, I have hereunto set my hand.

20 RALPH C. SHERMUND. 

